Insulating material and body composed thereof.



No Drawing.

UNITED STATES PATENT OFFICE,

ALBERT CHAMPION AND TAINE G. MODOUGAL, OF FLINT, MICHIGAN, ASSIGNORS TOCHAMPION IGNITION COMPANY, OF FLINT, MICHIGAN, A CORPORATION OFMICHIGAN.

INSULATING MATERIAL ANDQBODY COMPOSED THEREOF.

To all whom it may concern:

Be it known that we, ALBERT CHAMPION and TAINE G. MCDOUGAL, citizens ofthe Republic of France and the United States of America, respectively,and residents of Flint, county of Genesee, State of Michigan, haveinvented certain new and useful Improvements in Insulatin Material and'Body Composed Thereof, f which the fol lowing 1s a specification.

Our invention relates to the manufacture of spark plugs designed for usewith internal combustion engines, and particularly to the insulatingmembers used in and forming a part of such devices. One object of ourinvention is to provide an insulating member which will have improveddielectric strength, under the high temperature condi tions present ininternal combustion engines and will possess a structure which willenable it to better resist sudden changes in temperature Withoutcracking.

With the above and other objects in view, our invention consists: First:in an insulating member for the purpose stated in which the proportionof clay to the other ingredi ents used in the finished member and uponwhich its i nsulating properties depend, is increased, and in which theproportion of those substances which have to be mixed with the clay inthe practical manufacture of insulators (and which ordinarily have adeleterious efiect thereupon so far as concerns' the insulatingproperties, when used at higher temperatures, of the finished prod not),is reduced to a minimum. Second: in i an insulating member which, duringthe,

manufacture thereof is subjected to a higher firing temperature than hasheretofore been usual, made necessary bythe new prop'or-, tioning of theingredients used in order to maintain a vitrified structure. Third: insuch other improvements in and relating to insulating members for sparkplugs as will hereinafter appear.

Our inventionnot only includes an insulating member for 'a spark plug asa new article of manufacture, the same being made from a plasticcomposition made up of certain materials hereinafter enumerated, but

, it also includes the porcelain material per se made from thecomposition or mixture disclosed, which material is capable of usePatented Apr. 9, 1918.

Wherever high insulating qualities at high temperatures are desirable inan article or device to be made therefrom, and the method or process ofmaking insulating members for spark plugs from a composition made up ofthe ingredients specified, by subjecting the same to suitable operationsduring and as steps in the manufacture of the said members from thecomposition disclosed.

The insulating members of spark plugs for use in internal combustionengines are ordinarily formed from a composition comprising plastic clayor kaolin mixed with a certain portion of non-plastic and more or lessfusible materials and molded or shaped into proper form, and then dried,and finally subjected to a high temperature, or fired, to Vitrify themass. The plasticity of the mass is made possible on account of its rawclay content.

The non-plastic material (ordinarily reduce and control the shrinkage ofthe molded members and to prevent the formation of cracks therein duringthe drying thereof at a comparatively low temperature, and before theyare subjected to the firing process, during which the uncombined wateris driven oif (but not the water heldin chemical combination in theclay) also to prevent abnormal shrinkage and distortion during thevitrifying process. Fusible material (ordinarily feldspar) is used topromote vitrification of the mass during the firing process, thusproducing a hard, strong and compact finished product, the feldsparbeing melted at a lower temperature than any of the other ingredients.

The less the quantity of' the morefusible material present in themixture from which the insulating members are formed, the

plugs because it reduces the insulating properties thereof at the highertemperatures.

It therefore follows that a minimum vper cent. referred to above.

amount-of feldspar is desirable, because of its direct effect inreducing the insulating qualities at higher temperaturesof the finishedinsulator, due to its mere presence, and because vitrified bodiesobtained (usually at lower heats) through high feldspar content havebeen found to poorly resist breakage under suddenly varymg temperatures.

It is found in practice that a quantity of raw clay equal to about sixtyper cent. of the composition or mixture employed should be used in orderto secure the requisite plasticity to permit the various molding,lathing, kneading and other operations necessary to give the propershape and form to the insulators, while a quantity of feldspar equal toabout ten per cent. or as little as five per cent. of the compositionwill be suflicient to secure a proper vitrification thereof when theyare subjected to the correct firing process and will at the same timenot seriousl lower the insulating qualities of the insu ators.This'quantit has been found to secure the best balance between anunavoidable impairment of insulating qualities in the finishedproduct'due to the presence of feldspar therein on the one hand, and thenecessity for an excessivel high firing temperature due to an inor inatereductitliln of, the quantity of feldspar used on the ot er.

From the above it will be appreciated that there remains an unassignedquantity equal to 40% of the composition from which the insulators aremade, which deficiency is su plied by the non-plastic materials here inefore referred to, as it has been found in practice that non-plasticmaterial to the extent of about 40% of the composition is necessary toprevent crackin and undue shrinkage of the molded an shaped insulatingmembers during the drying operation or step to which they are subjectedbefore firing. If flint, alone, is used to' make up 30% or 35% of this40% then the fired insulators would not be uniform or homogeneous instructure, the flint being present in much the same condition as whenintroduced, because the flint is but slowly soluble in the moltenfeldspar during the firing operation.

Our invention, therefore, contemplates the use of calcined clay as thenon-plastic ingredient of the composition employed for making theinsulating members, either alone or in. connection with a much smallerquantity of flint than the thirty or thirty-five It follows that theamount of flint in the finished product is greatly reduced and theamount of clay upon which substitution the insulating qualities atincreased temperatures of the members is dependent is proportionatelyincreased. For example, and still assuinin the 60% proportion of raw oruncalcin clay and 10% of feldspar, then if 20% of calcined clay is usedthe amount of flint is reduced to 10%; and if calcined clay and feldsparalone are'used as the non-plastic constituents of the composition, thenthe flint is eliminated altogether.

It will be appreciated that the calcined clay is produced by heating rawor ordinary plastic clay to such a temperature that the chemicallycombined water held there- 15 in is driven off. This heattreatment ofthe cla causes it to lose its plastic qualities and to ecome an inert ornon-plastic substance. As this clay will not thereafter combine withwater, the uncombined water, which is ordinarily contained in theuncalcined clay, and is therefore present in the ingredients employed,will facilitate the operations necessary to give the proper form to Eheinsulating members before drying and Finally both the raw or uncalcinedclay and the calcined clay are in precisely the same condition, and arein all respects alike after the firing process has been performed, sothat the finished insulating members made in accordance with ourinvention are made up entirely of clay vitrified by the use of say 10%or less each of feldspar and flint, if flint is used at all.

In making an insulator for spark plugs in accordance with our inventionthe proper quantities of raw or uncalcined clay, calcincd clay (andflint or other non-plastic material if any such is used) and feldspar,are mixed and ground together in any suitable grinding mill until theproper degree of fineness is obtained and an intimate mixture has beensecured. After grinding the insulating members are properly formed fromthe mixture by any suitable molding, shaping, forming or similaroperations. The sa1d members are next dried at a comparatively lowtemperature to eliminate the water held in mechanical suspension in thecomposition from which they are formed, and which was either present inthe raw clay or was added during the operations anterior to the finalproduction of the formed insulating members in order to facilitate theworking of the composition.

- The body is then fired at the required temperature which exceeds by 40centi grade or more that used in common porcelain manufacture.

Having thus described and explained our invention, we claim and desireto secure by Letters Patent:

1, As a new article of manufacture, an insulating member for a sparkplug made from porcelain, and in which calcined clay is usedaszanon-plastic ingredient of the composition from which the said memberis formed.

2. As a new article of manufacture, an insulating member for a sparkplug formed from a mixture containing plastic uncalcined clay,non-plastic calcined clay, and a fusible vitrifying material.

3. As a new article of manufacture, an insulating member for a sparkplug formed from a mixture containing plastic uncalcined clay,non-plastic calcined clay, and feldspar.

4. As a new article of manufacture, an insulating member for a sparkplug formed from a mixture comprising plastic uncalcined clay, anon-plastic material made up of calcined clay and flint, and a fusibleVitrifying material.

5. As a new article of manufacture, an insulating member for a sparkplug formed from a -mixture comprising plastic uncalcined clay, anon-plastic material made up of calcined clay and'flint, and feldspar.

6. As anew article of manufacture, an insulating member for a spark plugformed from a mixture comprising approximately 60% of plastic uncalcinedclay, approximately 10% of a fusible vitrifying material, andapproximately of non-plastic ma terial some of which is calcined clay.

7. As a new article of manufacture, an insulating member for a sparkplug fdrmed from a mixture comprising approximately 60% of plasticuncalcined clay, approximately 10% of feldspar, and approximately 30% ofnon-plastic material some of which is calcined clay.

8. The insulating material herein described and made from a mixturecomprising approximately 60% of plastic uncalcined clay, approximately10% of fusible vitrifying material, and approximately 30% of non-plasticmaterial some of which is calcined clay.

. 9. The insulating material herein described and made from a mixturecomprising approximately 60% of plastic uncalcined clay, approximately10% of a fusible vitrifying material, and approximately 30% ofnon-plastic material made up of calcined clay and flint.

10. The insulating material herein described and made from a mixturecomprisingapproximately 60% of plastic uncalcined clay, approximately10% of feldspar, and approximately 30% of n0n-plastic material some ofwhich is calcined clay.

11. The insulating material herein described and made from a mixturecomprising approximately 60% of plastic uncalcined clay, approximately10% of feldspar, and approximately 30% of non-plastic material made upof calcined clay and flint.

In witness whereof we have hereunto set our hands at Flint, county ofGenesee, State of Michigan, this 17th day of August, 1917 ALBERTCHAMPION. TAINE G. MGDOUGAL.

